1. Field of the Invention
The present invention relates to a speaker which is used mainly as a receiver of a mobile communication equipment such as a portable telephone.
2. Description of the Prior Art
Conventionally, there is a narrow rectangular speaker in which a rectangular inner magnet type magnetic circuit, and a diaphragm to which a rectangular voice coil driven by the magnetic circuit is fixed are held on a rectangular frame. In such a speaker, the rectangular inner magnet type magnetic circuit is configured by: a rectangular yoke which is held by the frame; a magnet which is joined to the bottom face of the yoke, and which has a rectangular plate-like shape; and an upper plate which is joined to the upper face of the magnet, and which has a rectangular plate-like shape, and a rectangular magnetic gap into which the rectangular voice coil is to be fitted is formed between the inner wall face of the yoke and the outer side face of the upper plate. When an audio signal current is supplied to the voice coil, the diaphragm to which the voice coil is fixed is vibrated by an electromagnetic action with a magnetic field in the magnetic gap, to generate a sound or a voice. Examples of such a speaker are disclosed in Japanese Patent Application Laying-Open Nos. 2003-37895 and 2003-37890.